Thika, some good questions there, I am not sure about any legality that prevents it, I think the reason being that no one really has them yet as they are just starting to surface in SA now from what I know.
Like i mentioned my boat only gets used on Gamtoos and I am yet to see a boat there with them (the underwater lights), so it will be interesting to see if the reaction is good or bad as I do 90% of my fishing at night.
I just think the price for these lights are not suitable for the SA market, or at least the big brand models like Ocean LED, Lumitec, Lumishore etc in my opinion.
Regarding the side lights, Ocean LED have an HD through hull mounted light available at something crazy like $3000 per light, these are flush mounted into the hull to almost be a part of the boat, I believe there are the only lights that can be mounted on the side or below the boat. All other lights or from what I know are not advised to be mounted on the side.
I guess there are multiple benefits mounting them at the back for lots of reasons, like I also mentioned I am yet to switch mine one, never mind fit them but by next weekend I will have that done and will report back.
Just on that, different colors penetrate better in different types of water, blue I heard is best for fishing and green shows the best in murky water for example.
For mounting options below the waterline, you can pretty much only rig them to shine straight out, unless you have a surface that caters for mounting them at an angle, if you look at most of the pictures on line, you will see most of the people fit 2 - 4 lights depending on the boat size, at the back of the transom facing or shining backwards and you mount them about 2 inches below the water line.
I am no expert in this, this is just what I have gathered so far.